WO2003106097A1

WO2003106097A1 - Arc welding glare shielding device

Info

Publication number: WO2003106097A1
Application number: PCT/IT2002/000393
Authority: WO
Inventors: Giuseppe Pirola; René WERTHMULLER
Original assignee: Trexim S.R.L
Priority date: 2002-06-13
Filing date: 2002-06-13
Publication date: 2003-12-24
Also published as: DE60214439D1; EP1513647A1; AU2002314535A1; WO2003106097A9; EP1513647B1

Abstract

A glare shielding device includes at least one liquid-crystal shield (6); a non-optical sensor (3) supplying a first signal (S_M) related to a quantity associated with the formation of an electric arc; a control circuit (15) connected to the sensor (3) and to the shield (6) to control the shield (6) on the basis of the first signal (S_M); and a waveform recognition circuit (8, 11, 12) connected between the sensor (3) and the control circuit (15).

Description

ARC WELDING GLARE SHIELDING DEVICE

TECHNICAL FIELD The present invention relates to an arc welding glare shielding device.

BACKGROUND ART

As is known, welding masks or helmets currently feature glare shielding devices, which are selectively dimmed when exposed to potentially harmful light sources, but remain substantially transparent under normal conditions . Such devices comprise one or more liquid- crystal (LCD) shields, and optoelectronic sensors for detecting sparks associated with the formation of electric arcs when welding. When the intensity of the incident light on the optoelectronic sensors exceeds a given, normally adjustable, activation threshold, LCD shields are dimmed more or less instantaneously to protect the user's eyes. On the other hand, when not welding, i.e. in the absence of sparks caused by the formation of electric arcs, dimming of the LCD shields ceases, and the user has normal vision, even wearing the safety helmet or mask. Shields employing optoelectronic sensors, however, have serious drawbacks. That is, optoelectronic sensors must be exposed directly at all times to the light source (i.e. electric arcs) for shielding, and, if an opaque object is interposed between them and the source, the intensity of the incident light is drastically reduced, and may not be sufficient to dim the LCD shields . Moreover, even if not struck directly by the light emitted by the arcs during welding, various degrees of eye damage can still be caused by reflected glare. On the other hand, if the activation threshold is set too low, ambient light intensity may also be sufficient to dim the LCD shields, which therefore afford little advantage. In other words, potentially hazardous situations occur if the welding electrode is not visible at all times by the optoelectronic sensors .

By way of a solution to the problem, Patent US-A- 5,880,793 proposes using a combination of optoelectronic sensors, and non-optical sensors for detecting quantities other than light intensity but nevertheless related to the formation of arcs, such as magnetic field strength, which, as is known, is significantly disturbed when arc welding. In the solution described in the above patent, for each quantity detected, a respective independently adjustable activation threshold is established; and the LCD shields are dimmed when at least one of the activation thresholds is exceeded. The non-optical sensor must be enabled beforehand by the optoelectronic sensor. More specifically, upon the optoelectronic sensor detecting a welding arc spark, the non-optical sensor is enabled at least for a predetermined time interval, during which the LCD shields are controlled on the basis of signals supplied by both sensors, and then the non- optical sensor is again disabled.

This, however, only provides a partial solution to the problem, in that, whereas electromagnetic field strength sensors provide for detecting an arc even with obstacles in between, LCD shields can easily be dimmed by extraneous electromagnetic fields present in numerous environments. In fact, it is rarely possible to simply adjust the activation threshold to eliminate interference, while at the same time ensuring adequate user protection, so that the non-optical sensors must be disabled, as described above, when welding is not in progress, and use made initially of the optoelectronic sensors. In other words, in many cases, using non-optical sensors is not sufficient in itself to eliminate the drawbacks of shielding devices with optoelectronic sensors alone. And in any case, a combination of both optoelectronic and non-optical sensors must be used. DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a glare shielding device designed to eliminate the aforementioned drawbacks .

According to the present invention, there is provided a glare shielding device comprising: at least one liquid-crystal shield; a non-optical sensor supplying a first signal related to a quantity associated with the formation of an electric arc,-, and a control circuit connected to said sensor and to said shield to control said shield on the basis of said first signal; characterized by comprising waveform recognition means connected between said sensor and said control circuit.

Parameters associated with waveforms generated by welding arcs can thus be calculated and controlled; and the problems posed using optoelectronic sensors are eliminated by eliminating the need for a straight, clear path between the source of the detected quantity (arc) and the sensor. In other words, the user is safely protected even if the arc is accidentally concealed from the sensor when welding. Moreover, eliminating the optoelectronic sensors makes for a compact device. BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a three-quarter top view in perspective of a welding helmet equipped with a glare shielding device;

Figure 2 shows a simplified block diagram of a glare shielding device in accordance with a first embodiment of the present invention;

Figures 3a and 3b show graphs of quantities relative to the Figure 2 device;

Figure 4. shows a simplified block diagram of a glare shielding device in accordance with a second embodiment of the present invention;

Figure 5 shows a three-quarter top view in perspective of a welding machine housing part of the Figure 4 device. BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in Figure 1 indicates as a whole a welding helmet equipped with a glare shielding device 2. More specifically, device 2 is a liquid-crystal, selectively dimmed type. As shown in Figure 2, • device 2 comprises a non- optical sensor 3; a preprocessing stage 8; a logic unit 4; a drive circuit 5; and a liquid-crystal shield 6; and a manual control 7 is connected to a control input 4a of logic unit 4. In a preferred embodiment of the invention, sensor 3, which is located close to shield 6 on helmet 1, is a magnetic field strength sensor, and supplies at its output 3a an analog signal S_M related to the strength of a magnetic field M in which sensor 3 is immersed. A number of magnetic sources, including the electric arcs formed when welding, contribute to determining the strength of the magnetic field. More specifically, the formation of such electric arcs produces variations in magnetic field strength with frequencies normally ranging between 100 Hz and 3 MHz. Output 3a of sensor 3 is connected to an input of preprocessing stage 8.

More specifically, preprocessing stage 8 comprises an amplifying stage 8a and an envelope detector 8b cascade-connected to each other. Amplifying stage 8a receives analog signal S_M from sensor 3 , and supplies envelope detector 8b with an amplified analog signal S^. Envelope detector 8b, in itself known, is preferably a peak detector, and supplies an analog envelope signal S_E at its output connected to the detecting input 4b of logic unit 4. Analog envelope signal S_B is related in known manner to amplified analog signal S^. More specifically, analog envelope signal S_B substantially follows the leading edges of amplified analog signal S^, but has damped trailing edges and decreases more slowly (see Figure 3) .

Logic unit 4 comprises an analog-digital converter 10; an estimating stage 11; a comparator 12; a reference- generating block 13 ; and a control circuit 15. More specifically, analog-digital converter 10 is connected between detecting input 4b - to receive analog envelope signal S_E - and estimating stage 11, which has an output connected to a first input 12a of comparator 12. Analog- digital converter 10 samples analog envelope signal S_B, and supplies a digital envelope signal S_B' .

Estimating stage 11 determines in known manner the rise times T_R of envelope signal S_E - i.e. as shown in Figure 3b, the time taken by analog envelope signal S_E to increase by a predetermined quantity V, e.g. 0.5 V, from a minimum point - and supplies first input 12a of comparator 12 with a numeric value indicating rise time T_R.

Comparator 12 has a second input 12b connected to an output of reference-generating block 13 , which supplies a threshold time interval T_TH (e.g. 1 ms) which can be set by means of manual control 7; and an output connected to control circuit 15 and supplying a control signal S_c having a first logic value (e.g. high) when rise time T_R is greater than threshold time interval T_TH, and conversely a second logic value (low) .

Control circuit 15 is connected to drive circuit 5, which has an output connected to shield 6 and supplying a drive signal S_p related to control signal S_c.

During welding, sensor 3 detects disturbance of the magnetic field caused by the formation of electric arcs, and supplies analog signal S_M, the leading and trailing edges of which are enhanced and damped respectively by preprocessing stage 8. More specifically, the analog envelope signal S_B supplied by envelope detector 8b is related to the maximum amplitude of analog signal S_M and, therefore, to electromagnetic field strength, so that the amplitude peaks of the electromagnetic field produced by formation of a welding arc can be determined accurately by filtering disturbance from different sources, and any obstacles between the arc and sensor 3 are not sufficient to significantly shield disturbance of the magnetic field caused by formation of the arc.

Via drive circuit 5, control circuit 15 controls shield 6 on the basis of envelope signal S_B and, consequently, on the basis of the form of analog signal

S_M. More specifically, in the presence of a welding arc, envelope signal S_B (or, equivalently, S_B') has rapid leading edges; in which case, rise time T_R is greater

- than threshold time interval T_TH, control signal S_c is high, and control circuit 15 enables and dims shield 6 to protect the user. Conversely, when the welding arc ceases, envelope signal S_E decreases, so that rise time T_R is considered zero, control signal S_c is low, and control circuit 5 restores shield 6 to the rest condition in which it is substantially transparent. Transition to the rest state may take place immediately upon control signal S_c switching to the low logic value, or control circuit 15 may interpose a standby interval of given length to be on the safe side. In other words, preprocessing stage 8, estimating stage 11, and comparator 12 form a waveform recognition circuit for determining envelope signal S_E patterns associated with the formation of welding arcs. More specifically, in the presence of a rapid increase in envelope signal S_E (caused by a rapid increase in electromagnetic field strength) , a welding-arc-related event is determined, and shield 6 is therefore dimmed.

Alternatively, estimating stage 11 determines the maximum positive variation in envelope signal S_E within a predetermined time window. In which case, reference- generating block 13 supplies comparator 12 with a threshold amplitude value; and, if the maximum positive variation in envelope signal S_E exceeds the threshold amplitude value, comparator 12 sets control signal S_c to the high logic value, and conversely to the low logic value .

In other words, in this case, estimating circuit 11 estimates the time derivative of envelope signal S_B; and, when the derivative exceeds a given threshold, a welding- arc-related event is determined and shield 6 dimmed as described above.

Figures 4 and 5 show a further embodiment of the invention, in which any parts identical with those already described are indicated using the same reference numbers. In this case, a glare shielding device 20 comprises a chemical species, e.g. ozone, concentration sensor 21 located at a welding electrode 22 of a welding machine 23 (Figure 5) and connected to a transmitting, e.g. radio-wave, circuit 25, to which sensor 21 supplies an analog signal S_M' related to the ozone concentration around sensor 21. Device 20 also comprises a receiving circuit 26 located on helmet 1, close to shield 6 (at a distance from transmitting circuit 25) , and connected to preprocessing stage 8. Receiving circuit 26 receives analog signal S_M' from transmitting circuit 25, and supplies it to preprocessing stage 8, which, as before, amplifies analog signal S_M' to determine envelope signal S_E, which is then sampled; and estimating stage 11 calculates rise time T_R, on the basis of which control circuit 15 controls shield 6. Clearly, changes may be made to the device as described herein without, however, departing from the scope of the present invention.

In particular, any type of non-optical sensor can be used to determine a quantity related to the formation of electric arcs when welding, e.g. sensors operating in various frequency bands substantially ranging between 100 Hz and 3 MHz, such as radio-frequency sensors. The comparator may be replaced with an adjustable-gain amplifier. The device may even comprise other components for preprocessing the signal before sampling, particularly when the signal from the sensor is transmitted from a distance. And finally, the transmitting and receiving circuits may be of a different type and, in particular, connected by optical fibers.

Claims

1) A glare shielding device comprising: at least, one liquid-crystal shield (6); a non-optical sensor (3; 20) supplying a first signal (S_M; S_M') related to a quantity associated with the formation of an electric arc,- and a control circuit (15) connected to said sensor (3) and to said shield (6) to control said shield (6) on the basis of said first signal (S_M; S_M'); characterized by comprising waveform recognition means (8, 11, 12) connected between said sensor (3) and said control circuit (15) .

2) A device as claimed in Claim 1, characterized in that said waveform recognition means (8, 11, 12) comprise an envelope detector (8b) for determining the envelope of said first signal (S_M; S_M') and supplying a second signal (S_B) related to the envelope of said first signal.

3) A device as claimed in Claim 2, characterized in that said envelope detector (8b) is a peak detector.

4) A device as claimed in Claim 2 or 3, characterized in that said waveform recognition means (8, 11, 12) comprise an estimating circuit (11) for estimating a rise time (T_R) of said second signal (S_E) . 5) A device as claimed in Claim 4, characterized in that said waveform recognition means (8, 11, 12) comprise a comparing stage (12) for comparing said rise time (T_R) with a predetermined threshold time (T_TH) . 6) A device as claimed in Claim 5, characterized by comprising a control stage (15) connected to said comparing stage (12) and to said shield (6) to dim said shield (6) when said rise time (T_R) is less than said threshold time (T_TH) .

7) A device as claimed in Claim 2, characterized by comprising derivative means (11) for estimating a time derivative of said second signal.

8) A device as claimed in Claim 7, characterized in that said control circuit is connected to said derivative means (11) and to said shield (6) to dim said shield (6) when said time derivative exceeds a predetermined threshold.

9) A device as claimed in any one of the foregoing Claims, characterized in that said sensor (3) is a magnetic sensor.

10) A device as claimed in Claim 9, characterized in that said sensor (3) is located close to said shield (6) .

11) A device as claimed in any one of Claims 1 to 8, characterized in that said sensor (21) is a chemical species concentration sensor.

12) A device as claimed in Claim 11, characterized in that said sensor (21) is an ozone concentration sensor. 13 ) A device as claimed in any one of the foregoing Claims, characterized by comprising a transmitting circuit (25) and a receiving circuit (26) , which are interposed between said sensor (21) and said waveform recognition means (8, 11, 12) to respectively transmit and receive said first signal (S_M' ) over a distance.

14) A welding helmet comprising a glare shielding device (2; .20), characterized in that said glare shielding device (2; 20) is as claimed in any one of Claims 1 to 13.

15) A welding kit comprising a welding machine (22) having a welding electrode (23) ; and a welding helmet (1) having a glare shielding device (2; 20); characterized in that said glare shielding device (2; 20) is as claimed in Claim 13; and in that said sensor (21) and said transmitting circuit (25) are located close to said welding electrode (23) .